Origin: Greek
Used in a religious context, a prophet is one who speaks for the
gods, or God. Well known prophets are Jesus Christ and Muhammad (the
prophet of Islam and also the last prophet, according to believers).

Non-religiously, a prophet is a soothsayer or a fortune teller. For
example, the "prophet of doom" is used to describe one who is always
predicting, or expecting, bad things to happen.